Integral hydraulic power steering gears are known. "Integral" refers to a steering gear containing a manual steering mechanism, a hydraulic control valve assembly, and a hydraulic power cylinder integrated into a single unit.
The hydraulic power cylinder typically comprises a chamber divided into two chamber portions by a piston. The piston has a set of teeth which mesh with a sector gear fixed to an output shaft. The output shaft is connected via steering linkage to dirigible wheels of a vehicle to steer the vehicle when the output shaft is rotated.
The hydraulic control valve assembly controls the flow of pressurized hydraulic fluid between a hydraulic pump and one of the chamber portions to control the direction and amount of steering. The valve assembly typically comprises two relatively rotatable valve elements, one of which is connected to a rotatable input shaft coupled to the vehicle steering wheel. The other valve element is connected with a follow-up member, such as a ball screw drive, which rotates in response to movement of the piston. The ball screw drive provides a direct connection between the input shaft and the piston to allow for manual steering of the vehicle in the event of hydraulic fluid pressure loss.
It is desirable for such an integral hydraulic power steering gear to provide the driver of the vehicle with a physically perceptible indication of operation of the steering gear between a neutral steering condition, in which the vehicle is being driven in a straight line, and an actuated steering condition, in which the vehicle is being turned. It is known to use a detent mechanism to provide the aforementioned physically perceptible indication to the driver.